Need help with twitter cards, thumbnail is not displaying

Hello guys, I have a problem with meta tags for previews on social media. I’ve just developed a landing page and added the following meta tags (I’ve read that twitter can read from Open Graph meta tags dedicated to Facebook):

<meta property="og:title" content="Sonic Youth Review by Iren">
    <meta property="og:description" content="A Ranking of Albums of One of the Most Influential Rock Bands.">
    <meta property="og:image" content="img/screenshot.jpg">
    <meta property="og:url" content="">
    <meta name="twitter:card" content="summary_large_image">
    <meta name="twitter:site" content="@IrenSayWhen">
<meta name="twitter:image:alt" content="A photo of Sonic Youth members with a logo of the site, a title of the site saying Sonic Youth Album Rating and a site description saying A Ranking of Albums of One of the Most Influential Rock Bands.">

Facebook displaying everything as it should be, with appropriate thumbnail. But twitter doesn’t. It displays an ugly gray square instead. Firstly, I thought the problem is in lack of additional image meta tag for twitter and added this:

<meta property="twitter:image" content="img/screenshot.jpg">

But nothing changed. What’s wrong?

By the way, I tried to change my relative link img/screenshot.jpg to absolute link pointing to that image in my GitHub repo, but Twitter Card Validator says “WARN: The image URL specified by the ‘twitter:image’ metatag may be restricted by the site’s robots.txt file, which will prevent Twitter from fetching it.”
P.C. Sorry for my English, I’m not a native speaker. :upside_down_face: